when his team is way better then yours, they could compete with 4,5 half men. And yes lucky fans ain't total scrubs, but still weaker then the drafted players.
And as said before, the defence rotates also, so if you have an weak attacker his matchup will backup a bit an help more in the defense. (there was an BB statement long time ago, but i don't think they changed it with the engne changes) The same happens with a superior attacker, he draws exra attention from the defense, but also makes it easier to score for his team mates - i believe both effect are created through the ratings ;)
And overall a statistical evaluation needs more data to be good, in this case the lucky fan indeed was lucky ;)